It was Nadal's second straight title and his 47th straight clay-court victory. He beat world No. 1 Roger Federer in the final of the Monte Carlo Masters last Sunday.
The victory was Nadal's 47th straight on clay, passing the legendary Bjorn Borg of Sweden for the second-longest clay-court winning streak.
Guillermo Vilas of Argentina is tops on the list with 53 straight clay-court wins.
"I've achieved my main objective here, and I've overtaken Borg's number of wins and I guess I could try to go for Vilas' total in Rome," Nadal told the BBC. "But I have my sights set on Roland Garros."
The French Open is played at Roland Garros and starts on May 29.
Nadal improved his record for the season to 22-3.